Adhesive sheet

ABSTRACT

The adhesive sheet wound into a roll includes: a long release film; an adhesive layer provided in a label form on the release film; and a pressure-sensitive adhesive film having a label part covering the adhesive layer and provided so as to be in contact with the release film around the adhesive layer and a peripheral part surrounding an outside of the label part, wherein a through hole penetrating the pressure-sensitive adhesive film is provided outside a portion corresponding to a part of the adhesive layer intended to be attached to an adherend and inside the label part, and wherein outer circumference of the adhesive layer× 1/43≦maximum width of the through hole×number of the through holes per label part of the pressure-sensitive adhesive film≦outer circumference of the adhesive layer is satisfied.

TECHNICAL FIELD

The present invention relates to an adhesive sheet, and more particularly relates to an adhesive sheet having two functions of a dicing tape and a die bonding film.

BACKGROUND ART

Recently, an adhesive sheet has been developed, which has two functions of a dicing tape for fixing a semiconductor wafer to dice the semiconductor wafer into individual chips and a die bonding film (also referred to as a die attach film) for bonding the diced semiconductor chip to a lead frame, a package substrate, or the like or for stacking and bonding together the semiconductor chips in a stacked package.

As such an adhesive sheet, a precut adhesive sheet has been developed in consideration of workability such as attachability to a wafer or attachability to a ring frame before dicing (see, for example, Patent Literature 1).

An example of the precut adhesive sheet is shown in FIGS. 11, 12A and 12B. FIG. 11 is a diagram showing an adhesive sheet wound into a roll, FIG. 12A is a plan view of the adhesive sheet viewed from its pressure-sensitive adhesive film 53 side, and FIG. 12B is a sectional view taken along a line B-B of FIG. 12A. The adhesive sheet 50 includes a release film 51, an adhesive layer 52, and a pressure-sensitive adhesive film 53. The adhesive layer 52 is processed into a circular shape corresponding to the shape of a wafer, and has a circular label shape. The pressure-sensitive adhesive film 53 is formed by removing an area peripheral to a circular portion corresponding to the shape of a ring frame for dicing, and, as shown in the drawings, has a circular label part 53 a and a peripheral part 53 b surrounding the outside of the circular label part 53 a. The adhesive layer 52 and the circular label part 53 a of the pressure-sensitive adhesive film 53 are laminated together so that their centers are aligned, and the circular label part 53 a of the pressure-sensitive adhesive film 53 covers the adhesive layer 52 and is in contact with the release film 51 around the adhesive layer 52. The pressure-sensitive adhesive film 53 is generally formed by laminating a pressure-sensitive adhesive layer on a base film.

Before wafer dicing, the release film 51 is peeled off from the adhesive layer 52 and the pressure-sensitive adhesive film 53 laminated together, and as shown in FIG. 13, the backside of a semiconductor wafer W is attached onto the adhesive layer 52, and a ring frame F for dicing is adherently fixed to the outer periphery of the circular label part 53 a of the pressure-sensitive adhesive film 53. In this state, the semiconductor wafer W is diced. Then, the pressure-sensitive adhesive film 53 is subjected to curing treatment such as irradiation with ultraviolet rays, if necessary, and semiconductor chips are picked up. At this time, the pressure-sensitive adhesive film 53 is separated from the adhesive layer 52 so that the semiconductor chip is picked up with the adhesive layer 52 being attached to its backside. The adhesive layer 52 attached to the backside of the semiconductor chip then functions as a die bonding film when the semiconductor chip is bonded to a lead frame, a package substrate, or another semiconductor chip.

Meanwhile, the pressure-sensitive adhesive film 53 generally covers the adhesive layer 52 and is in contact with the release film 51 around the adhesive layer 52, but there is a case where air remains in a very narrow gap created between the release film 51 and the pressure-sensitive adhesive film 53 due to the thickness of the adhesive layer 52. This phenomenon is more remarkable when the adhesive layer 52 has a thickness as large as 65 μm or more or the pressure-sensitive adhesive film 53 has a high elastic modulus. Such air between the release film 51 and the pressure-sensitive adhesive film 53 does not cause a problem by itself, because the air may move and escape to the outside of the circular label part 53 a and does not have a major impact on the physical properties of the pressure-sensitive adhesive film 53.

However, the adhesive sheet 50 is to be placed in a special environment whose temperature varies widely. For example, the adhesive sheet 50 is placed under cold conditions (e.g., −20° C. to 5° C.) during storage and transportation, heated when attached to the semiconductor wafer W, and placed under ordinary temperature conditions when used to process the semiconductor wafer W. Such a temperature change causes major dimensional changes in the release film 51, the adhesive layer 52, and the pressure-sensitive adhesive film 53, and therefore there is a case where air enters between the adhesive layer 52 and the pressure-sensitive adhesive film 53 so that a void is formed. There is a fear that the void causes defective attachment to the semiconductor wafer W and reduces yield in the subsequent semiconductor wafer W dicing process, chip pick-up process, and chip bonding process. It is to be noted that in this specification, the term air refers to air between a pressure-sensitive adhesive film and a release film or between an adhesive layer and a release film, and the term void refers to air between an adhesive layer and a pressure-sensitive adhesive film.

As described above, the void reduces yield and is formed between the adhesive layer 52 and the pressure-sensitive adhesive film 53 and is therefore difficult to remove, which is a very serious problem for the adhesive sheet 50. Further, in light of the principle of void formation, air is more likely to develop into a void when its amount is larger. For this reason, the amount of air is preferably reduced.

As a measure to suppress void formation, a laminated sheet has been disclosed (see, for example, FIGS. 1 and 2 in Patent Literature 2), which has through holes provided so as to penetrate a base film and a pressure-sensitive adhesive layer of a pressure-sensitive adhesive film in the thickness direction of the pressure-sensitive adhesive film. By providing such through holes in the pressure-sensitive adhesive film, it is possible to prevent void formation between an adhesive layer and the pressure-sensitive adhesive film, and therefore it can be expected that the occurrence of defective attachment to a semiconductor wafer will be effectively suppressed.

CITATION LIST Patent Literatures

Patent Literature 1: JP 2007-2173 A

Patent Literature 2: JP 2008-153587 A

SUMMARY OF INVENTION Technical Problem

However, in the case of the adhesive sheet disclosed in Patent Literature 2, the number of the through holes is as small as 4 to 30, and therefore there is a case where air with potential to develop into voids or formed voids cannot be completely discharged.

Particularly, large-diameter wafers are used to produce MPUs with a large chip size or memories (DRAMs, flash memories) required to be mass-produced to reduce costs. In this case, the sizes of an adhesive layer and a pressure-sensitive adhesive film of an adhesive sheet are increased depending on the size of a wafer, and therefore the area of a part of the adhesive sheet where void formation should be prevented is also increased, and when the number of through holes provided in the adhesive sheet is small, the through holes have a limitation in discharging voids.

Further, flip-chip mounting is performed to mount a semiconductor device on a circuit board by face-down bonding. In recent years, the use of a wafer-processing tape in such flip-chip mounting has been proposed. In this case, an adhesive layer of the wafer-processing tape needs to have a certain degree of thickness to fill gaps between projecting electrodes of a semiconductor device or a gap between steps formed by wiring in the surface of a circuit board. When the adhesive layer has a large thickness, a large gap is created between a pressure-sensitive adhesive film and a release film attached together around the outer edge of the adhesive layer. This increases the amount of air remaining in the gap. Also in this case, when the number of through holes provided in the wafer-processing tape is small, the through holes have a limitation in discharging air or voids developed from air.

In order to solve the problem, the number of through holes may be increased, but merely increasing the number of through holes may cause a problem that air adversely enters from outside via through holes.

It is therefore an object of the present invention to provide an adhesive sheet that can effectively suppress void formation between an adhesive layer and a pressure-sensitive adhesive film to reduce the occurrence of defective attachment to a semiconductor wafer.

Solution to Problem

In order to achieve the above object, the present invention is directed to an adhesive sheet wound into a roll, including: a long release film; an adhesive layer provided in a label form on the release film; and a pressure-sensitive adhesive film having a label part covering the adhesive layer and provided so as to be in contact with the release film around the adhesive layer and a peripheral part surrounding an outside of the label part, wherein a through hole penetrating the pressure-sensitive adhesive film is provided outside a portion corresponding to a part of the adhesive layer intended to be attached to an adherend and inside the label part, and wherein outer circumference of the adhesive layer× 1/43≦maximum width of the through hole×number of the through holes per label part of the pressure-sensitive adhesive film≦outer circumference of the adhesive layer is satisfied.

Further, it is preferred that in the adhesive sheet, the number of the through holes per label part of the pressure-sensitive adhesive film is 1 or more but 400 or less.

Further, it is also preferred that in the adhesive sheet, the maximum width of the through hole is 0.01 mm or more but 50 mm or less.

Further, it is also preferred that in the adhesive sheet, the adhesive layer has a thickness of 65 μm or more.

Further, it is also preferred that in the adhesive sheet, the adhesive layer has a diameter of 215 mm or more.

Further, it is also preferred that in the adhesive sheet, the pressure-sensitive adhesive film has a linear expansion coefficient of 400 ppm/K or less.

Further, it is also preferred that the adhesive sheet has s support member provided outside the label part of the pressure-sensitive adhesive film along a longitudinal direction.

Advantageous Effects of Invention

According to the present invention, it is possible to effectively suppress void formation between the adhesive layer and the pressure-sensitive adhesive film and therefore to reduce the occurrence of defective attachment to a semiconductor wafer.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a plan view schematically showing the structure of an adhesive sheet according to an embodiment of the present invention, and FIG. 1B is a sectional view taken along a line A-A of FIG. 1A.

FIG. 2 is a plan view schematically showing the structure of a modified example of the adhesive sheet according to the embodiment of the present invention.

FIG. 3 is a plan view schematically showing the structure of another modified example of the adhesive sheet according to the embodiment of the present invention.

FIG. 4 is a plan view schematically showing the structure of another modified example of the adhesive sheet according to the embodiment of the present invention.

FIG. 5 is a plan view schematically showing the structure of another modified example of the adhesive sheet according to the embodiment of the present invention.

FIG. 6 is a plan view schematically showing the structure of another modified example of the adhesive sheet according to the embodiment of the present invention.

FIG. 7 is a plan view schematically showing the structure of another modified example of the adhesive sheet according to the embodiment of the present invention.

FIG. 8A is a plan view schematically showing the structure of an adhesive sheet according to another embodiment of the present invention, and FIG. 8B is a sectional view taken along a line A-A of FIG. 8A.

FIGS. 9A to 9E are diagrams showing the shape of through holes provided in an adhesive sheet according to Example or Comparative Example of the present invention.

FIGS. 10A to 10C are diagrams showing a place where through holes are provided in an adhesive sheet according to Example or Comparative Example of the present invention.

FIG. 11 is a schematic perspective view of a conventional adhesive sheet wound into a roll.

FIG. 12A is a plan view showing the structure of the conventional adhesive sheet, and FIG. 12B is a sectional view taken along a line B-B of FIG. 12A.

FIG. 13 is a sectional view showing a state where the conventional adhesive sheet and a ring frame for dicing are attached together.

DESCRIPTION OF EMBODIMENTS First Embodiment

Hereinbelow, embodiments of the present invention will be described in detail based on the accompanying drawings. FIG. 1A is a plan view of an adhesive sheet according to an embodiment of the present invention viewed from its pressure-sensitive adhesive film side, and FIG. 1B is a sectional view taken along a line A-A of FIG. 1A.

As shown in FIGS. 1A and 1B, the adhesive sheet 10 is a wafer processing tape including a long release film 11, an adhesive layer 12, and a pressure-sensitive adhesive film 13 and having two functions of a dicing tape and a die bonding film.

The adhesive layer 12 is provided on a first surface of the release film 11 and has a circular label shape corresponding to the shape of a wafer. The pressure-sensitive adhesive film 13 has a circular label part 13 a covering the adhesive layer 12 and provided so as to be in contact with the release film 11 around the adhesive layer 12 and a peripheral part 13 b surrounding the outside of the circular label part 13 a. The peripheral part 13 b may be one completely surrounding the outside of the circular label part 13 a or one incompletely surrounding the outside of the circular label part 13 a as shown in FIGS. 1A and 1B. The circular label part 13 a has a shape corresponding to a ring frame for dicing.

Hereinbelow, each of the components of the adhesive sheet 10 according to this embodiment will be described in detail.

(Release Film)

The release film 11 used in the adhesive sheet 10 according to the present invention is not particularly limited, and a well-known one such as a polyethylene terephthalate (PET)-based film, a polyethylene-based film, or a release-treated film can be used. The thickness of the release film 11 is not particularly limited and may be appropriately set, but is preferably 25 μm to 75 μm.

(Adhesive Layer)

As described above, the adhesive layer 12 according to the present invention is provided on the release film 11 and has a circular label shape corresponding to the shape of a wafer. The shape corresponding to the shape of a wafer may be a shape substantially the same as the shape of a wafer and substantially the same in size as the wafer, or alternatively may be a similar shape substantially the same as the shape of a wafer but larger in size than the wafer. The shape corresponding to the shape of a wafer does not always need to be a circle, but is preferably close to a circle, more preferably a circle.

The adhesive layer 12 is attached to the backside of a chip when the chip is picked up after a semiconductor wafer is attached to the adhesive layer 12 and diced, and is used as an adhesive to fix the chip to a substrate or a lead frame. As the adhesive layer 12, for example, a pressure-sensitive adhesive containing at least one selected from an epoxy-based resin, an acrylic resin, and a phenol-based resin can be preferably used. Besides the above, a polyimide-based resin or a silicone-based resin can also be used. The thickness of the adhesive layer may be appropriately set, but is preferably about 5 μm to 100 μm.

(Pressure-Sensitive Adhesive Film)

As described above, the pressure-sensitive adhesive film 13 according to the present invention has the circular label part 13 a having a shape corresponding to the shape of a ring frame for dicing and the peripheral part 13 b surrounding the outside of the circular label part 13 a. Such a pressure-sensitive adhesive film can be formed by removing an area peripheral to the circular label part 13 a from a film-shaped pressure-sensitive adhesive by precut processing. The shape corresponding to the shape of a ring frame for dicing is a similar shape substantially the same as the shape of the inside of a ring frame but larger in size than the inside of the ring frame. The shape corresponding to the shape of a ring frame does not always need to be a circle, but is preferably close to a circle, more preferably a circle.

As shown in FIGS. 1A and 1B, the pressure-sensitive adhesive film 13 has circular through holes 14. The through holes 14 are provided so as to penetrate the pressure-sensitive adhesive film 13 and to be in contact with the outer edge of the adhesive layer 12.

Further, the through holes 14 are provided so that the maximum width of the through holes 14×the number of the through holes 14 per label part 13 a of the pressure-sensitive adhesive film 13 satisfies outer circumference of the adhesive layer 12× 1/43≦maximum width×number≦outer circumference of the adhesive layer 12.

If the maximum width of the through holes 14×the number of the through holes 14 is smaller than the outer circumference of the adhesive layer 12× 1/43, air with potential to develop into voids or formed voids cannot be completely discharged. If the maximum width of the through holes 14×the number of the through holes 14 is larger than the outer circumference of the adhesive layer 12, air enters from outside via the through holes 14.

The place of the through holes 14 is not limited to a place in contact with the outer edge of the adhesive layer 12, but the through holes 14 shall be provided outside a portion corresponding to a part 15 of the adhesive layer 12 intended to be attached to an adherend and inside the circular label part 13 a. For example, as shown in FIG. 2, the through holes 14 may be provided radially from a place in the pressure-sensitive adhesive film 13 corresponding to the outer edge of the part 15 of the adhesive layer 12 intended to be attached to an adherend. Also in this case, the through holes 14 need to be provided so that the maximum width of the through holes 14×the number of the through holes 14 per label part 13 a of the pressure-sensitive adhesive film 13 satisfies outer circumference of the adhesive layer 12× 1/43≦maximum width×number≦outer circumference of the adhesive layer 12. It is to be noted that in this modified example, the circular through holes 14 are radially arranged, but the through holes 14 may be provided randomly in a place including a portion corresponding to the outside of the part 15 of the adhesive layer 12 intended to be attached to an adherend and the inside of the circular label part 13 a.

Here, the phrase “outside a portion corresponding to the part 15 of the adhesive layer 12 intended to be attached to an adherend and inside the circular label part 13 a” refers to a region R extending from a place in the pressure-sensitive adhesive film 13 corresponding to the outer edge of the part 15 of the adhesive layer 12 intended to be attached to an adherend to the outer edge of the circular label part 13 a.

Further, the part 15 of the adhesive layer 12 intended to be attached to an adherend is a place where a semiconductor wafer is to be attached when the semiconductor wafer is diced using the adhesive sheet 10, and is located, for example, 10 mm to 25 mm inside the outer edge of the adhesive layer 12.

The through holes are intended to discharge a void itself that causes defective attachment to a semiconductor wafer or air at a stage prior to development into a void. For such a purpose, a void or air needs to be discharged to the outside of the part 15 of the adhesive layer 12 intended to be attached to a semiconductor wafer (adherend). When the through holes 14 are provided only in a portion corresponding to the inside of the part 15 of the adhesive layer 12 intended to be attached to an adherend or only in a portion corresponding to the outside of the circular label part 13 a of the pressure-sensitive adhesive film 13, air remaining in a gap created between the release film 11 and the pressure-sensitive adhesive film 13 due to the thickness of the adhesive layer 12 or a void formed between the adhesive layer 12 and the pressure-sensitive adhesive film 13 by the entry of air due to dimensional changes in the release film 11, the adhesive layer 12, and the pressure-sensitive adhesive film 13 caused by temperature change cannot be discharged to the outside of the part 15 of the adhesive layer 12 intended to be attached to an adherend. For this reason, the through holes 14 need to be provided outside a portion corresponding to the part 15 of the adhesive layer 12 intended to be attached to an adherend and inside the circular label part 13 a.

Further, providing the through holes 14 in a place corresponding to the outside of the adhesive layer 12 makes it possible to guide air so that the air travels in a direction toward the outside of the adhesive layer 12, which makes it possible to minimize the possibility that air enters between the adhesive layer 12 and the pressure-sensitive adhesive film 13 and develops into a void. Further, providing the through holes 14 in a portion in contact with the outer edge of the adhesive layer 12 is more effective, because this makes it possible not only to reduce the possibility that air develops into a void but also to immediately discharge air generated at the outer edge of the adhesive layer 12 to reduce air itself. Therefore, when the number of the through holes 14 needs to be minimized, the through holes 14 are preferably provided only in a portion in contact with the outer edge of the adhesive layer 12.

Further, the through holes 14 do not always need to be provided along the entire outer edge of the adhesive layer 12. As shown in FIG. 3, the through holes 14 may be provided within an area of ±60° or less around the center of the adhesive layer 12 with respect to a straight line a passing through the center of the adhesive layer 12 and perpendicular to the longitudinal direction of the release film 11 (i.e., within a region R inside a line b-c and a region R′ inside a line d-e shown in FIG. 3). Alternatively, the through holes 14 may be provided within an area of ±45° or less around the center of the adhesive layer 12 with respect to the straight line a.

The shape of the through holes 14 is not limited to a circle as long as a void can be discharged, and may be a triangle, a rhombus, a line shape, or the like. However, from the viewpoint of preventing contamination of the adhesive layer 12, the through holes 14 preferably have a line shape. The through holes having a line shape may be, for example, through holes 141 having a straight line shape as shown in FIG. 4, wavy through holes 142 as shown in FIG. 5, U-shaped through holes 143 as shown in FIG. 6, or V-shaped through holes 144 as shown in FIG. 7.

The orientation of the through holes 14 is a design choice, but as will be described below, the present inventors have found a preferred orientation by experiment. More specifically, when the through holes have a circular shape or a regular polygonal shape, the orientation of the through holes is arbitrarily set. When the through holes have a shape other than “a circular shape or a regular polygonal shape” and when the through holes have a line shape or a wavy shape, the orientation of the through holes shall be set so that the longitudinal direction of the through holes is as parallel as possible to a tangent to the circle of label of the adhesive layer 12 or the pressure-sensitive adhesive film 13. When the through holes have a U-shape or a V-shape, the orientation of the through holes shall be set so that the convex side of the through holes is directed to the outside of the circle of the label. This makes it possible to easily discharge a void toward the outside.

It is to be noted that in FIGS. 4 and 5, the through holes 141 and 142 are provided so that their longitudinal direction is parallel to a tangent to the circle of label of the adhesive layer 12 or the pressure-sensitive adhesive film 13, but may be provided so that their longitudinal direction is parallel to a tangent to the circle of label of the adhesive layer 12 or the pressure-sensitive adhesive film 13. In this case, the through holes may be continuously provided so as to elongate in the region R.

Further, a combination of the above-described place and shape of the through holes 14 may be appropriately selected.

The maximum width of the through holes 14 is preferably 50 mm or less, more preferably 0.01 mm or more but 10 mm or less, even more preferably 0.1 mm or more but 5 mm or less. If the maximum width is less than 0.01 mm, a void is less likely to be discharged and if the maximum width exceeds 50 mm, air is likely to enter from the outside of the pressure-sensitive adhesive film 13 and therefore there is a risk that void formation is adversely induced. When the through holes have a line shape, the maximum width refers to a length from start point to endpoint, and when the through holes have a shape other than a line shape, the maximum width refers to the longest distance within the hole.

The number of the through holes 14 is preferably 1 or more but 400 or less, more preferably 2 or more but 300 or less, even more preferably 6 or more but 250 or less per circular label part 13 a of the pressure-sensitive adhesive film 13. If the number of the through holes 14 exceeds 360, air is likely to enter from the outside of the release film 11, and therefore there is a risk that void formation is adversely induced.

Further, when the number of the through holes 14 per circular label part 13 a of the pressure-sensitive adhesive film 13 is an even number, arranging the through holes 14 so that they are symmetrical about the center of the adhesive layer 12 makes it possible to easily discharge air and to obtain a great void formation-suppressing effect.

The pressure-sensitive adhesive film 13 is not particularly limited as long as a difference in linear expansion coefficient between the release film 11 and the pressure-sensitive adhesive film 13 is 250 ppm/K or less, but shall have sufficient adhesive power during wafer dicing to prevent detachment of a wafer and have low adhesive power during picking-up of chips after dicing so as to be easily separated from the adhesive layer. For example, one obtained by providing a pressure-sensitive adhesive layer on a base film can be appropriately used.

The pressure-sensitive adhesive film 13 preferably has a linear expansion coefficient of 400 ppm/K or less, more preferably 345 ppm/K or less, even more preferably 290 ppm or less. By setting the linear expansion coefficient to 400 ppm/K or less, shrinkage at low temperature can be suppressed, and particularly when the through holes 14 have a linear shape, the through holes 14 can be prevented from opening during cold storage and transportation and therefore the entry of air from outside can be prevented, which makes it possible to more effectively prevent void formation. It is to be noted that when the linear expansion coefficient exceeds 400 ppm/K, the through holes 14 open and air enters from outside during cold storage and transportation even when the through holes 14 have a linear shape, but there is no problem because air itself does not cause defective attachment to a semiconductor wafer, and even when air develops into voids, there is no problem as long as the voids are discharged via the through holes.

The base film of the pressure-sensitive adhesive film 13 is not particularly limited as long as the pressure-sensitive adhesive film 13 can have a linear expansion coefficient of 400 ppm/K or less. However, when a radiation curable material is used as the pressure-sensitive adhesive layer that will be described later, the base film preferably has radiotransparency.

Examples of the material of the base film include: homopolymers and copolymers of α-olefins such as polyethylene, polypropylene, ethylene-propylene copolymers, polybutene-1, poly-4-methylpentene-1, ethylene-vinyl acetate copolymers, ethylene-ethyl acrylate copolymers, ethylene-methyl acrylate copolymers, ethylene-acrylic acid copolymers, and ionomers and mixtures of two or more of them; and thermoplastic elastomers such as polyurethane, styrene-ethylene-butene or pentene-based copolymers, and polyamide-polyol copolymers and mixtures of two or more of them. Alternatively, the base film may be made of a mixture of two or more materials selected from the group consisting of the above-mentioned materials, and may be a single-layered or multi-layered film made of the two or more materials.

The thickness of the base film is not particularly limited and may be appropriately set, but is preferably 50 μm to 200 μm.

A resin used for the pressure-sensitive adhesive layer of the pressure-sensitive adhesive film 13 is not particularly limited as long as the pressure-sensitive adhesive film 13 can have a linear expansion coefficient of 400 ppm/K or less, and a well-known resin used as a pressure-sensitive adhesive such as a chlorinated polypropylene resin, an acrylic resin, a polyester resin, a polyurethane resin, or an epoxy resin can be used. It is preferred that the resin used for the pressure-sensitive adhesive layer 13 is mixed with an acrylic pressure-sensitive adhesive, a radiation-polymerizable compound, a photopolymerization initiator, a curing agent, etc., if necessary to prepare a pressure-sensitive adhesive. The thickness of the pressure-sensitive adhesive layer 13 is not particularly limited and may be appropriately set, but is preferably 5 μm to 30 μm.

Addition of a radiation-polymerizable compound to the pressure-sensitive adhesive layer makes it easy to separate the pressure-sensitive adhesive layer from the adhesive layer by radiation curing. As the radiation-polymerizable compound, for example, a low-molecular-weight compound is used, which has at least two photopolymerizable carbon-carbon double bonds in its molecule that can forma three-dimensional network by light irradiation.

More specifically, trimethylolpropane triacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, dipentaerythritol monohydroxypentaacrylate, dipentaerythritol hexaacrylate, 1,4-butylene glycol diacrylate, 1,6-hexanediol diacrylate, polyethylene glycol diacrylate, or oligoester acrylate can be used.

Besides the above-mentioned acrylate-based compounds, an urethane acrylate-based oligomer can also be used. The urethane acrylate-based oligomer is obtained by reacting a polyester- or polyether-type polyol compound and a polyfunctional isocyanate compound (e.g., 2,4-tolylenediisocyanate, 2,6-tolylenediisocyanate, 1,3-xylylenediisocyanate, 1,4-xylylenediisocyanate, or diphenylmethane-4,4-diisocyanate) to obtain an isocyanate-terminated urethane prepolymer and then reacting the isocyanate-terminated urethane prepolymer and a hydroxyl group-containing acrylate or methacrylate (e.g., 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, polyethylene glycol acrylate, polyethylene glycol methacrylate). The pressure-sensitive adhesive layer may be made of a mixture of two or more selected from the above resins.

When a photopolymerization initiator is used, for example, isopropylbenzoin ether, isobutylbenzoin ether, benzophenone, Michler's ketone, chlorothioxanthone, dodecylthioxanthone, dimethylthioxanthone, diethylthioxanthone, benzyl dimethyl ketal, α-hydroxycyclohexyl phenyl ketone, or 2-hydroxymethylphenylpropane can be used. The amount of such a photopolymerization initiator to be added is preferably 0.01 to 5 parts by mass with respect to 100 parts by mass of an acrylic copolymer.

Hereinbelow, a method for producing the adhesive sheet 10 according to this embodiment will be described.

First, a laminated body is prepared, in which the long pressure-sensitive adhesive film 13 is attached by lamination to the long release film 11 having the adhesive layer 12 with a circular label shape corresponding to the shape of a wafer. It is to be noted that the adhesive layer 12 with a circular label shape may be formed by applying an adhesive varnish onto the release film 11, drying the adhesive varnish, and performing precut processing by stamping the adhesive varnish into a circle and peeling off an unnecessary portion around the circular portion from the release film 11.

Then, precut processing is performed by making cuts in the laminated body from the pressure-sensitive adhesive film 13 side to the middle of the release film 11 in the thickness direction of the release film 11 by a cutting die and peeling off the pressure-sensitive adhesive film 13 from the release film 11 so that the circular label part 13 a and the peripheral part 13 b remain.

The through holes may be formed by any method, but are preferably formed concurrently with precutting of the adhesive layer and/or the pressure-sensitive adhesive film. Allowing a blade for precutting to have a blade for forming the through holes 14 makes it possible to form the through holes 14 concurrently with precutting, which makes the process simple. Further, by forming the through holes 14 concurrently with precutting of the adhesive layer 12, air removal can also be performed by utilizing cutting pressure applied during precutting of the pressure-sensitive adhesive film 13 performed later or nip rolls on a path line.

Second Embodiment

Hereinbelow, a second embodiment will be described. An adhesive sheet 10′ according to this embodiment has the same structure as the adhesive sheet according to the first embodiment except that a support member 16 is provided, and the same production method as described above with reference to the first embodiment can be applied.

Hereinbelow, the difference from the first embodiment will be described. As shown in FIG. 8A, the support member 16 is provided at both ends of the release film 11 in the short direction of the release film 11.

The thickness of the support member 16 shall be equal to or larger than a thickness corresponding to a difference in level between an area in which the adhesive layer 12 and the circular label part 13 a of the pressure-sensitive adhesive film 13 are laminated together on the release film 11 and the peripheral part 13 b of the pressure-sensitive adhesive film 13, that is, equal to or larger than the thickness of the adhesive layer 12. When the support member has such a thickness, a space is created between the pressure-sensitive adhesive film 13 and a second surface of the release film 11 that overlaps the surface of the pressure-sensitive adhesive film 13 when the adhesive sheet 10 is rolled up, which makes it easy to remove a void formed between the adhesive layer and the pressure-sensitive adhesive film.

It is to be noted that the position of the support member 16 is not limited to both ends of the release film 11 in the short direction of the release film 11, and the support member 16 may be provided anywhere as long as the position of the support member 16 corresponds to the outside of the label part 13 a of the pressure-sensitive adhesive film 13. However, from the viewpoint of preventing a transfer mark from being formed on the soft surface of the adhesive layer 12 due to a level difference between an area where the adhesive layer 12 and the circular label part 13 a of the pressure-sensitive adhesive film 13 or the support member 16 are laminated together and the peripheral part 13 b of the pressure-sensitive adhesive film 13 when the adhesive sheet is wound into a roll to be prepared as a product, the support member 16 is preferably provided in a region R′ extending from both ends of the release film 11 in the short direction of the release film 11 to the adhesive layer 12.

Further, the support member 16 is preferably provided on the second surface of the release film 11 opposite to the first surface of the release film 11 on which the adhesive layer 12 and the pressure-sensitive adhesive film 13 are provided.

When being provided at both ends of the release film 11 in the short direction of the release film 11, the support member 16 can be made intermittent or continuous along the longitudinal direction of the release film 11. However, from the viewpoint of more effectively suppressing the formation of a transfer mark, the support member 16 is preferably provided continuously along the longitudinal direction of the base film 11.

As the support member 16, for example, a pressure-sensitive adhesive tape obtained by applying a pressure-sensitive adhesive onto a resin film base material can be appropriately used. By attaching such a pressure-sensitive adhesive tape to a predetermined position at both ends of the second surface of the release film 11, the adhesive sheet 10′ according to this embodiment can be formed. The pressure-sensitive adhesive tape to be attached may be single-layered or may be formed by laminating thin tapes.

The resin film base material of the pressure-sensitive adhesive tape is not particularly limited, but, in terms of heat resistance, smoothness, and availability, is preferably selected from polyethylene terephthalate (PET), polypropylene, and high-density polyethylene. The composition and physical properties of the pressure-sensitive adhesive of the pressure-sensitive adhesive tape are not particularly limited as long as the pressure-sensitive adhesive tape is not separated from the release film 11 in the rolling-up process and storage process of the adhesive sheet 10.

EXAMPLES

Hereinbelow, the present invention will be described in more detail based on examples, but is not limited to these examples.

Pressure-sensitive adhesive compositions and adhesive compositions were prepared in the following manner, and adhesive sheets were prepared by the following methods and their performance was evaluated.

(Preparation of Pressure-Sensitive Adhesive Composition)

<Pressure-Sensitive Adhesive Composition 1>

A mixture of 340 g of isooctyl acrylate, 13 g of methyl methacrylate, 60 g of hydroxyacrylate, 0.5 g of methacrylic acid, and benzoyl peroxide as a polymerization initiator was added to 400 g of toluene as a solvent while the amount of the mixture dropped to the toluene was appropriately adjusted, and reaction temperature and reaction time were adjusted to obtain a solution of a compound (1) having a weight average molecular weight of 800,000. Then, 2 parts by weight of CORONATE L (manufactured by Nippon Polyurethane Industry Co., Ltd.) as polyisocyanate and 300 parts by weight of ethyl acetate as a solvent with respect to 100 parts by weight of the compound (1) in the solution were added to the solution of the compound (1) with stirring to obtain a pressure-sensitive adhesive composition 1.

<Pressure-Sensitive Adhesive Composition 2>

2.5 grams of 2-isocyanate ethyl methacrylate as a compound having radiation curable carbon-carbon double bond and functional group and hydroquinone as a polymerization inhibitor were added to the solution of the compound (1) while the amount of the hydroquinone dropped to the solution was appropriately adjusted, and reaction temperature and reaction time were adjusted to obtain a solution of a compound (2) having a radiation curable carbon-carbon double bond. The Tg of the compound (2) was measured by DSC and was found to be −49° C. Then, 2 parts by weight of CORONATE L as polyisocyanate, 1 part by weight of IRGACURE 184 (manufactured by Nihon Ciba-Geigy K.K.) as a photopolymerization initiator, and 300 parts by weight of ethyl acetate as a solvent with respect to 100 parts by weight of the compound (2) in the solution were added to the solution of the compound (2) with stirring to obtain a pressure-sensitive adhesive composition 2.

(Preparation of Pressure-Sensitive Adhesive Film)

<Pressure-Sensitive Adhesive Film 1A>

The pressure-sensitive adhesive composition 1 was applied onto a release film constituted from a release-treated polyethylene terephthalate film to achieve a dry film thickness of 25 μm and dried at 110° C. for 3 minutes, and was then attached to an 80 μm-thick low-density polyethylene film extruded at 180° C. to prepare a pressure-sensitive adhesive film 1A having a linear expansion coefficient of 260 ppm/K. The linear expansion coefficient was measured using a thermomechanical analyzer (manufactured by Rigaku Corporation) under the following conditions, and was determined in the range of −20° C. to +20° C.

<<Measurement Conditions>>

Instrument: TMA8310 manufactured by Rigaku Corporation

Temperature range: −30° C. to 50° C.

Temperature rise rate: 5° C./min

Measuring load: 49 mN

Atmosphere gas: N2

<Pressure-Sensitive Adhesive Film 1B>

The pressure-sensitive adhesive composition 1 was applied onto a release film constituted from a release-treated polyethylene terephthalate film to achieve a dry film thickness of 10 μm and dried at 110° C. for 3 minutes, and was then attached to an 80 μm-thick ethylene-vinyl acetate copolymer film extruded at 180° C. to prepare a pressure-sensitive adhesive film 1B having a linear expansion coefficient of 300 ppm/K. The linear expansion coefficient was measured in the same manner as described above.

<Pressure-Sensitive Adhesive Film 1C>

The pressure-sensitive adhesive composition 2 was applied onto a release film constituted from a release-treated polyethylene terephthalate film to achieve a dry film thickness of 10 μm and dried at 110° C. for 3 minutes, and was then attached to a 100 μm-thick vinyl chloride film extruded at 170° C. to prepare a pressure-sensitive adhesive film 1C having a linear expansion coefficient of 380 ppm/K. The linear expansion coefficient was measured in the same manner as described above.

<Pressure-Sensitive Adhesive Film 1D>

The pressure-sensitive adhesive composition 2 was applied onto a release film constituted from a release-treated polyethylene terephthalate film to achieve a dry film thickness of 5 μm and dried at 110° C. for 3 minutes, and was then attached to an 80 μm-thick vinyl chloride film extruded at 190° C. to prepare a pressure-sensitive adhesive film 1D having a linear expansion coefficient of 420 ppm/K. The linear expansion coefficient was measured in the same manner as described above.

(Release Film)

<Release Film 2A>

A release-treated polyethylene terephthalate film having a thickness of 38 μm was used. The linear expansion coefficient of the film was measured using a thermomechanical analyzer (manufactured by Rigaku Corporation) in the same manner as the measurement of the linear expansion coefficient of the pressure-sensitive adhesive film, and was found to be 60 ppm/K.

(Preparation of Adhesive Composition)

<Adhesive Composition>

A composition containing 15 parts by mass of a cresol novolac-type epoxy resin (epoxy equivalent: 197, molecular weight: 1200, softening point: 70° C.), 70 parts by mass of acrylic resin SG-P3 (manufactured by Nagase Chemtex Corporation, mass average molecular weight: 850,000, glass transition temperature: 12° C.), 15 parts by mass of a phenol novolac resin (hydroxyl group equivalent: 104, softening point: 80° C.) as a curing agent, and 1 part of CUREZOL 2PZ (manufactured by SHIKOKU CHEMICALS CORPORATION, trade name: 2-phenylimidazole) as an accelerator was mixed with cyclohexanone with stirring and further kneaded using a bead mill for 90 minutes to obtain an adhesive composition.

(Formation of Adhesive Layer)

<Adhesive Layer A>

The adhesive composition was applied onto the release film 2A to achieve a dry film thickness of 65 μm and heat-dried at 110° C. for 1 minute to form a coating film in B-stage (intermediate stage during curing of thermosetting resin). In this way, an adhesive layer 3A was obtained. The adhesive layer 3A was cold-stored.

<Adhesive layer B>

The adhesive composition was applied onto the release film 2A to achieve a dry film thickness of 120 μm and heat-dried at 110° C. for 1 minute to form a coating film in B-stage (intermediate stage during curing of thermosetting resin). In this way, an adhesive layer 3B was obtained. The adhesive layer 3B was cold-stored.

(Preparation of Adhesive Sheet)

The cold-stored release film 2A having the adhesive layer 3A formed thereon was returned to ordinary temperature, and precut processing was performed by adjusting the depth of a cut made in the release film 2A to 15 μm or less so that the adhesive layer 3A was cut into a circle having a diameter of 320 mm (circumference: about 1005 mm). Then, an unnecessary portion of the adhesive layer 3A was removed, and the pressure-sensitive adhesive film 10 was laminated on the release film 2A at room temperature so that the pressure-sensitive adhesive layer thereof came into contact with the adhesive layer 3A. Then, precut processing was performed by adjusting the depth of a cut made in the release film 2A to 15 μm or less so that the pressure-sensitive adhesive film 10 was cut into a circle having a diameter of 370 mm so as to be concentric with the adhesive layer, and at the same time, 256 through holes having a shape shown in FIG. 9A were provided in the pressure-sensitive adhesive film 10 so as to be located in a place shown in FIG. 10A. In this way, an adhesive sheet for 12-inch wafer of Example 1 was prepared.

Adhesive sheets according to Examples 2, 4 to 12, and 14 to 18 and Comparative Examples 2 and 4 to 6 were prepared in the same manner as in Example 1 in accordance with combinations shown in the following Tables 1 to 4.

The cold-stored release film 2A having the adhesive layer 3A formed thereon was returned to ordinary temperature, and precut processing was performed by adjusting the depth of a cut made in the release film 2A to 15 μm or less so that the adhesive layer 3A was cut into a circle having a diameter of 220 mm (circumference: about 691 mm). Then, an unnecessary portion of the adhesive layer 3A was removed, and the pressure-sensitive adhesive film 10 was laminated on the release film 2A at room temperature so that the pressure-sensitive adhesive layer thereof came into contact with the adhesive layer 3A. Then, precut processing was performed by adjusting the depth of a cut made in the release film 2A to 15 μm or less so that the pressure-sensitive adhesive film 10 was cut into a circle having a diameter of 270 mm so as to be concentric with the adhesive layer, and at the same time, 200 through holes having a shape shown in FIG. 9A were provided in the pressure-sensitive adhesive film 1C so as to be located in a place shown in FIG. 10B. In this way, an adhesive sheet for 8-inch wafer of Example 3 was prepared.

Adhesive sheets according to Example 13 and Comparative Examples 1 and 3 were prepared in the same manner as in Example 3 in accordance with combinations shown in the following Tables 3 and 4.

Here, the through holes shall be provided so that outer circumference of the adhesive layer× 1/43≦maximum width of the through holes×number of the through holes≦outer circumference of the adhesive layer is satisfied. This means that when “(maximum diameter of the through holes×number of the through holes)/outer circumference of the adhesive layer” is defined as L, L needs to satisfy 0.0233≦L≦1. The values of L of Examples and Comparative Examples were determined. The results are shown in Tables 1 to 4.

It is to be noted that a through hole shown in FIG. 9A has a linear shape having a maximum width (length from start point to end point) of 0.1 mm, a through hole shown in FIG. 9B has a circular shape having a maximum width (diameter) of 1 mm, a through hole shown in FIG. 9C has an arc shape having a maximum width (length from start point to end point) of 0.06 mm, a through hole shown in FIG. 9D has a V shape having a maximum width (length from start point to end point) of 30 mm, and a through hole shown in FIG. 9 (e) has a linear shape having a maximum width (length from start point to end point) of 2 mm.

The through holes were provided at regular intervals in a place shown in FIGS. 10A to 10C in the pressure-sensitive adhesive layer.

The place shown in FIG. 10A in which through holes are provided is a portion corresponding to the outer edge of the adhesive layer, that is, a region Ra shown by a solid line in FIG. 10A. The place shown in FIG. 10B in which through holes are provided is a portion that corresponds to the outer edge of the adhesive layer and that is within an area of ±60° or less around the center of the adhesive layer with respect to a straight line a passing through the center of the adhesive layer and perpendicular to the longitudinal direction of the release film, that is, a region Rb shown by a solid line in FIG. 10B. The place shown in FIG. 10C in which through holes are provided is a portion that corresponds to the outer edge of the adhesive layer and that is within an area of ±45° or less around the center of the adhesive layer with respect to a straight line a passing through the center of the adhesive layer and perpendicular to the longitudinal direction of the release film, that is, a region Rc shown by a solid line in FIG. 10C.

(Characteristics Evaluation Test)

The adhesive sheets of Examples 1 to 18 and Comparative Examples 1 to 6 were subjected to a characteristics evaluation test in the following manner.

<Evaluation of Void Formation-Suppressing Ability>

Each of the adhesive sheets of Examples and Comparative Examples was wound into a roll having 300 circular pressure-sensitive adhesive films to prepare an adhesive sheet roll. The obtained adhesive sheet rolls were stored in a refrigerator (5° C.) for 1 month and were then wrapped, packed, and put in a transport truck to make a round trip between Hiratsuka and Kobe (about 1,000 km). The container of the truck was kept cold at −20° C. by dry ice. Then, the adhesive sheet rolls were unpacked and returned to ordinary temperature, and then were unwrapped to evaluate the ability of the adhesive sheets of Examples and Comparative Examples to suppress void formation. The adhesive sheets were visually observed to determine whether or not void formation occurred, and their ability to suppress void formation was evaluated according to the following four criteria ⊙, ∘, Δ, and x.

⊙ (excellent): No voids and no air were observed from every angle by the naked eye.

∘ (good): Air was observed between the pressure-sensitive adhesive film and the release film.

Δ (acceptable): Air was observed between the adhesive layer and the release film.

x (defective): Void formation was observed between the adhesive layer and the pressure-sensitive adhesive film.

The result of the above test of each of Examples and Comparative Examples is shown in Tables 1 to 4.

TABLE 1 Example Example Example Example Example Example 1 2 3 4 5 6 Through Place Pressure- Pressure- Pressure- Pressure- Pressure- Pressure- hole sensitive sensitive sensitive sensitive sensitive sensitive adhesive adhesive adhesive adhesive adhesive adhesive film film film film film film FIG. 10A FIG. 10B FIG. 10B FIG. 10C FIG. 10A FIG. 10B Shape FIG. 6A FIG. 6A FIG. 6A FIG. 6A FIG. 6B FIG. 6B Maximum 0.1 0.1 0.1 0.1 1 1 diameter (mm) Number 256 300 200 288 32 108 Pressure- Type 1A 1B 1B 1C 1C 1A sensitive CTE (ppm) 260 300 300 380 380 260 adhesive film Release film 2A 2A 2A 2A 2A 2A Adhesive Type 3A 3A 3A 3A 3A 3A layer L 0.0255 0.0298 0.0289 0.0286 0.0318 0.1074 Void formation-suppressing ⊙ ⊙ ⊙ ⊙ ⊙ ⊙ ability

TABLE 2 Example Example Example Example Example Example 7 8 9 10 11 12 Through Place Pressure- Pressure- Pressure- Pressure- Pressure- Pressure- hole sensitive sensitive sensitive sensitive sensitive sensitive adhesive adhesive adhesive adhesive adhesive adhesive film film film film film film FIG. 10C FIG. 10A FIG. 10B FIG. 10A FIG. 10B FIG. 10B Shape FIG. 6B FIG. 6D FIG. 6C FIG. 6E FIG. 6D FIG. 6A Maximum 1 30 0.06 2 30 0.1 diameter (mm) Number 192 32 400 360 2 320 Pressure- Type 1C 1A 1B 1B 1C 1C sensitive CTE (ppm) 380 260 300 300 380 380 adhesive film Release film 2A 2A 2A 2A 2A 2A Adhesive Type 3A 3A 3A 3A 3A 3B layer L 0.1910 0.9549 0.0239 0.7162 0.0597 0.0318 Void formation-suppressing ⊙ ⊙ ⊙ ⊙ ⊙ ⊙ ability

TABLE 3 Example Example Example Example Example Example 13 14 15 16 17 18 Through Place Pressure- Pressure- Pressure- Pressure- Pressure- Pressure- hole sensitive sensitive sensitive sensitive sensitive sensitive adhesive adhesive adhesive adhesive adhesive adhesive film film film film film film FIG. 10B FIG. 10B FIG. 10B FIG. 10B FIG. 10B FIG. 10B Shape FIG. 6C FIG. 6B FIG. 6A FIG. 6B FIG. 6A FIG. 6B Maximum 0.06 1 0.1 1 0.1 1 diameter (mm) Number 300 96 256 64 256 100 Pressure- Type 1C 1A 1D 1D 1D 1D sensitive CTE (ppm) 380 260 420 420 420 420 adhesive film Release film 2A 2A 2A 2A 2A 2A Adhesive Type 3B 3B 3A 3A 3B 3B layer L 0.0260 0.0955 0.0255 0.0637 0.0255 0.0995 Void formation-suppressing ⊙ ⊙ ∘ ∘ Δ Δ ability

TABLE 4 Comparative Comparative Comparative Comparative Comparative Comparative Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Through Place Pressure- Pressure- Pressure- Pressure- Pressure- Pressure- hole sensitive sensitive sensitive sensitive sensitive sensitive adhesive adhesive adhesive adhesive adhesive adhesive film film film film film film FIG. 10B FIG. 10B FIG. 10B FIG. 10B FIG. 10B FIG. 10B Shape FIG. 6E FIG. 6D FIG. 6A FIG. 6A FIG. 6A FIG. 6C Maximum 2 30 0.1 0.1 0.1 0.06 diameter (mm) Number 360 40 96 96 200 300 Pressure- Type 1A 1A 1C 1C 1B 1C sensitive CTE (ppm) 260 260 380 380 300 380 adhesive film Release film 2A 2A 2A 2A 2A 2A Adhesive Type 3A 3A 3A 3A 3A 3B layer L 1.0417 1.1937 0.0139 0.0095 0.0199 0.0179 Void x x x x x x formation-suppressing ability

As shown in Tables 1 and 2, in Examples 1 to 11, the through holes penetrating the pressure-sensitive adhesive film were provided so that the value of maximum diameter of through holes×number of through holes was within a prescribed range, and the linear expansion coefficient of the pressure-sensitive adhesive film was 400 ppm/K or less, and therefore, void formation was very successfully suppressed.

As shown in Tables 2 and 3, in Examples 12 to 14, the thickness of the adhesive layer was 120 μm that was much larger than that in Examples 1 to 11. However, the through holes penetrating the pressure-sensitive adhesive film were provided so that the value of maximum diameter of through holes×number of through holes was within a prescribed range, and the linear expansion coefficient of the pressure-sensitive adhesive film was 400 ppm/K or less, and therefore, void formation was very successfully suppressed.

As shown in Table 3, in Examples 15 and 16, the through holes penetrating the pressure-sensitive adhesive film were provided so that the value of maximum diameter of through holes×number of through holes was within a prescribed range, but the linear expansion coefficient of the pressure-sensitive adhesive film exceeded 400 ppm/K. Therefore, the entry of air between the pressure-sensitive adhesive film and the release film was observed, but void formation was successfully suppressed.

As shown in Table 3, in Examples 17 and 18, the through holes penetrating the pressure-sensitive adhesive film were provided so that the value of maximum diameter of through holes×number of through holes was within a prescribed range, but the linear expansion coefficient of the pressure-sensitive adhesive film exceeded 400 ppm/K and the thickness of the pressure-sensitive adhesive layer was 120 μm that was much larger than that in Examples 1 to 11, and therefore the entry of air between the adhesive layer and the release film was observed. When air enters between the adhesive layer and the release film, that is, inside the adhesive layer, there is a high risk that air enters also between the adhesive layer and the pressure-sensitive adhesive film so that void formation occurs. However, void formation was suppressed due to the void-discharging effect of the through holes.

On the other hand, as shown in Table 4, in Comparative Examples 1 and 2, the through holes penetrating the pressure-sensitive adhesive film were provided so that the value of maximum diameter of through holes×number of through holes exceeded a prescribed range. Therefore, the amount of air entering from outside was too large and air or voids developed from air could not be completely discharged, that is, void formation could not be satisfactorily suppressed.

As shown in Table 4, in Comparative Examples 3 to 6, the through holes penetrating the pressure-sensitive adhesive film were provided so that the value of maximum diameter of through holes×number of through holes was less than a prescribed range. Therefore, the number of the through holes was too small and air or voids developed from air could not be completely discharged, that is, void formation could not be satisfactorily suppressed.

As can be seen from these Examples and Comparative Examples, the adhesive sheet according to the present invention can suppress void formation between the adhesive layer and the pressure-sensitive adhesive film to reduce the occurrence of defective attachment to a semiconductor wafer.

REFERENCE SIGNS LIST

-   10, 10′: Adhesive sheet -   11: Release film -   12: Adhesive layer -   13: Pressure-sensitive adhesive film -   13 a: Circular label part -   13 b: Peripheral part -   14: Through hole -   15: Part intended to be attached to adherend -   16: Support member 

The invention claimed is:
 1. An adhesive sheet for an 8-inch wafer or a 12-inch wafer wound into a roll, the adhesive sheet comprising: a long release film; an adhesive layer provided in a label form on the release film; and a pressure-sensitive adhesive film having a label part covering the adhesive layer and provided so as to be in contact with the release film around the adhesive layer and a peripheral part surrounding an outside of the label part; wherein: a plurality of through holes penetrating the pressure-sensitive adhesive film are provided outside a portion corresponding to a part of the adhesive layer intended to be attached to the wafer; the portion of the adhesive layer intended to be attached to the wafer is 10 mm to 25 mm inside of an outer circumference of the adhesive layer and inside the label part; and the following relationship is satisfied: outer circumference of the adhesive layer× 1/43≦maximum through hole width×number of through holes per label part of the pressure-sensitive adhesive film≦outer circumference of the adhesive layer.
 2. The adhesive sheet according to claim 1, wherein the number of through holes per label part of the pressure-sensitive adhesive film is 2 or more but 400 or less.
 3. The adhesive sheet according to claim 1, wherein the maximum through hole width is 0.01 mm or more but 50 mm or less.
 4. The adhesive sheet according to claim 1, wherein the adhesive layer has a thickness of 65 μm or more.
 5. The adhesive sheet according to claim 1, wherein the adhesive layer has a diameter of 215 mm or more.
 6. The adhesive sheet according to claim 1, wherein the pressure-sensitive adhesive film has a linear expansion coefficient of 400 ppm/K or less.
 7. The adhesive sheet according to claim 1, which has a support member provided outside the label part of the pressure-sensitive adhesive film along a longitudinal direction.
 8. The adhesive sheet according to claim 1, wherein: the plurality of through holes are provided within portions of the label part of the pressure-sensitive adhesive film defined with respect to a straight line perpendicular to a longitudinal direction of the long release film and passing through a center of the adhesive layer label; and the portions include the straight line perpendicular to the longitudinal direction of the long release film and are bounded by straight lines that pass through the center of the adhesive layer label at angles of ±60° with respect to the straight line perpendicular to the longitudinal direction of the long release film.
 9. The adhesive sheet according to claim 1, wherein the plurality of through holes comprises through holes having a line shape.
 10. The adhesive sheet according to claim 1, wherein: the plurality of through holes comprises at least one of through holes having a line shape, through holes having a wavy shape, through holes having a U-shape, and through holes having a V-shape; the through holes having a line shape and the through holes having a wavy shape are oriented so that a longitudinal direction of each through hole is arranged substantially parallel to a tangent of an outer perimeter of the adhesive layer label; and the through holes having a U-shape and the through holes having a V-shape are oriented so that a convex end of each through hole is directed away from a center of the adhesive layer label.
 11. The adhesive sheet according to claim 1, wherein the plurality of through holes comprises through holes arranged symmetrically about a center of the adhesive layer label. 